The invention relates to improvements in power trains which can be utilized in motor vehicles for the transmission of torque from a prime mover (e.g., a combustion engine) to one or more driven parts such as the wheels of the vehicle. More particularly, the invention relates to improvements in power trains which embody infinitely variable transmissions of the type having first and second adjustable pulleys or sheaves and an endless flexible element which is trained over and serves to transmit torque between such sheaves.
Infinitely variable transmissions embodying two sheaves and an endless flexible torque transmitting element further comprise at least one adjusting unit for each of the adjustable sheaves to vary the friction (i.e., the clamping engagement) between the coaxial flanges of the respective adjustable sheave and the adjacent loop-shaped portion of the flexible element. As a rule, such power trains further comprise a hydromechanical torque monitoring device or sensor which transmits to at least one of the sheaves a portion of the torque being supplied by a prime mover. The torque sensor comprises at least one plenum chamber which receives pressurized hydraulic fluid from at least one surce (such as a gear pump or a vane pump). The outlet of the plenum chamber discharges fluid by way of one or more adjustable flow restrictors, e.g., by way of a throttle having at least two mobile valving elements disposed at the outlet of the plenum chamber and being movable relative to each other to an extent which is determined by the magnitude of applied torque to establish at least one fluid pressure serving to determine the magnitude of frictional clamping engagement between the flanges of the adjustable sheaves and the flexible element of the infinitely variable transmission.
Power trains of the above outlined character are disclosed, for example, in German patent No. 28 28 347 and in published German patent applications Nos. 40 36 683, 42 34 294, 42 01 692 and 35 38 884. In several of the power trains which are disclosed in the above enumerated publications, the fluid pressure which is selected by the torque sensor is dependent upon the applied torque as well as upon the load. It can be said that such torque sensors constitute or act not unlike torque- and/or transmission ratio dependent valves with throttling portions disposed downstream of the plenum chamber of the torque sensor. The plenum chamber receives pressurized hydraulic fluid from a pump and the throttling portion of the torque sensor is closed, at least in part, in response to detection of abrupt changes of transmitted torque. This entails a corresponding rise of pressure in the plenum chamber, and such rise of pressure is communicated to the fluid in the adjusting units for the sheaves of the infinitely variable transmission by way of suitable channels, conduits and/or other passages so that the adjusting units cause the respective sheaves to move into more or less pronounced frictional torque transmitting or torque receiving engagement with the adjacent portions of the endless flexible torque transmitting element of the transmission. In many instances, the adjusting units comprise hydraulic cylinder and piston arrangements.
The aforementioned valving elements of many known torque sensors are or resemble discs having confronting cam faces or tracks which preferably bear upon spherical and/or otherwise configurated rolling elements between them. The pressurized fluid in the plenum chamber of the torque sensor causes the valving elements to bear upon the rolling elements between them. When the transmitted torque undergoes an abrupt change, particularly when the torque which is being transmitted by a prime mover to the respective valving element abruptly develops a peak, te valving elements move away from each other in the axial direction of the torque sensor whereby one of these valving elements changes the rate at which pressurized fluid can flow from the plenum chamber.
The valving elements of the aforediscussed conventional torque sensors constitute a means for mechanically transmitting at least a portion of applied torque and for varying the fluid pressure in the plenum chamber (by varying the effective cross-sectional area of the outlet of the plenum chamber) in dependency upon changes of applied torque in order to influence the extent of frictional clamping engagement between the endless flexible element (e.g., a chain) and at least one adjustable sheave of the infinitely variable transmission.
It is also known to utilize the hydraulic fluid which leaves the plenum chamber of the torque sensor as a lubricant for the parts of the infinitely variable transmission.
The disclosure in commonly owned copending patent application titled: "Power Train with infinitely variable Ratio Transmission", Ser. No. 08/572,536, filed Dec. 14, 1995, inventor: Oswald Friedmann, Urban Panther and Ivo Agner, and the disclosure in the co-pending, commonly owned patent application titled: "Torque Monitoring Apparatus", Ser. No. 08/568,134, filed Dec. 6, 1995, now U.S. Pat. No. 5,711,730, inventors: Oswald Friedmann and Armin Veil, are both incorporated herein, in their entirety, by this reference.